One pot preparation of bimetallic catalysts for ethylene 1-olefin copolymerization

ABSTRACT

A process of forming a bimetallic catalyst composition comprising a cocatalyst (a trialkylaluminum compound) and a catalyst precursor. The precursor comprises at least two transition metals; a metallocene complex is a source of one of said two transition metals. The precursor is produced in a single-pot process by contacting a porous carrier, in sequence, with a dialkylmagnesium compound, an aliphatic alcohol, a non-metallocene transition metal compound, a contact product of a metallocene complex and a trialkyl-aluminum compound, and methylalumoxane.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a divisional U.S. Ser. No. 08/621,566, filed Mar.25, 1996, now U.S. Pat. No. 6,417,130, the entire disclosure of which isexpressly incorporated herein by reference.

FIELD OF THE INVENTION

The invention relates to the production of bimetallic ethylenepolymerization catalysts systems containing two sources of transitionmetals for the production of broad and/or bimodal molecular weightdistribution (MWD) polyethylene resins in a single reactor. In apreferred embodiment, the invention relates to the production oftitanium/zirconium-based bimetallic catalyst systems that produce broadand/or bimodal MWD polyethylene resins in a single reactor. The lowmolecular weight (LMW) polymer component in the resin is produced by theZr active centers, while the high molecular weight (HMW) polymercomponent is produced by the Ti active centers. The relativeproductivity of the two active centers determines the ratio of the HMWand the LMW polymer components in the final resin.

This invention particularly relates to a new procedure for preparingbimetallic catalysts. This procedure results in bimetallic catalystswith a more uniform inter-particle distribution of the metals whichproduce the HMW and LMW polymer components.

The uniform inter-particle distribution of the metals in the catalystresults in the reduction of gel particles in polyethylene film. Gelparticles are attributable to high molecular weight polymer componentswhich are substantially greater in molecular weight than the surroundingmatrix resin. The presence of gels in polyethylene film interfere withthe film-forming process, reduce film toughness properties and lower thefilm quality rating (FQR) and, hence, must be avoided.

SUMMARY OF THE INVENTION

This invention relates to supported bimetallic ethylene polymerizationcatalysts with improved inter-particle distribution of the Zr activecenters and facilitates the scale-up production of the catalyst. Thisinvention also includes a new procedure for preparing bimetalliccatalysts.

The invention relates to the production of bimetallic catalyst systemsfor ethylene polymerization containing two transition metals. Thesecatalysts produce broad/bimodal MWD polyethylene resins in a singlereactor. In a preferred embodiment, the invention relates to theproduction of titanium/zirconium-based bimetallic catalyst systems thatproduce broad/bimodal MWD polyethylene resins in a single reactor. TheLMW polymer component in the resin is produced by the Zr active centers,while the HMW polymer component is produced by the Ti active centers.The relative productivity of the two active centers determines the ratioof the HMW and the LMW polymer components in the final resin.

This invention includes a new procedure for preparing bimetalliccatalysts. Herein, bimetallic (containing two transition metals)catalyst precursors are produced without isolating the titaniumcomponent prior to introduction of the zirconocene component. Activatedbimetallic catalyst precursors exhibit good productivity and produceresins with a bimodal MWD. The low molecular weight polymer component inthe resin is produced by the zirconocene active centers while the highmolecular weight polymer component is produced by the Ti-based centers.Typically, the bimetallic catalyst precursor is prepared in two steps.First, the titanium component is prepared and isolated as a free-flowingpowder. Then the zirconium component is added to the titanium componentto form the final bimetallic catalyst precursor. The one-stageincorporation of each of the two metals onto a support to produce thebimetallic catalyst precursors of this invention greatly reduces thebatch time of the catalyst preparation. Moreover, in preferredbimetallic catalysts prepared according to this invention, the zirconiumcatalyst component is contacted with a trialkylaluminum compound such astrimethylaluminum (TMA) or triethylaluminum (TEAL) prior to addition tothe titanium catalyst component. This step is carried out in the absenceof methylalumoxane (MAO). Bimetallic catalysts prepared with thisprocedure have significantly higher activity than catalysts preparedwithout this particular step.

DESCRIPTION OF THE DRAWINGS

Each of FIGS. 1, 2, and 3 is a ¹³C NMR spectrograph. FIG. 1 depicts the¹³C NMR of (n-BuCp)₂ZrCl₂ in CDCl₃, FIG. 2 depicts (n-BuCp)₂ZrCl₂-TMA,1:10 solution in heptane and the spectrograph of FIG. 3 depicts(n-BuCp)₂ZrCl₂-TEAL, 1:10 solution in heptane.

DETAILED DESCRIPTION OF THE INVENTION

Catalyst Composition

The catalysts of the invention comprise a cocatalyst comprising analuminumalkyl compound, such as a trialkyl-aluminum compound which isfree of alumoxane, and a solid catalyst precursor comprising a carrier,an alumoxane, at least one metallocene transition metal source and anon-metallocene transition metal source. The loading of the firsttransition metal provided by a metallocene compound ranges from 0.01 to1.0 wt % metal in the final catalyst precursor, preferably from 0.10 to0.60 wt % metal and more preferably from 0.20 to 0.40 wt % metal; theloading of the second transition metal ranges from 0.10 to 10.0 wt %metal in the final catalyst precursor, preferably from 0.40 to 5.0 wt %metal and more preferably from 0.70 to 3.0 wt % metal. The twotransition metal sources exhibit different hydrogen responses underethylene polymerization conditions, and produce at least two polymercomponents of different molecular weights.

The carrier material for the catalyst is a solid, particulate, porous,preferably inorganic material, such as an oxide of silicon and/or ofaluminum. The carrier material is used in the form of a dry powderhaving an average particle size of from about 1 micron to about 500microns, preferably from about 10 microns to about 250 microns. Thesurface area of the carrier is at least about 3 square meters per gram(m²/g), and preferably from at least 50 m²/g up to 350 m²/g. The carriermaterial should be dry, that is, free of absorbed water. Drying of thecarrier material can be effected by heating at about 100° C. to about1000° C., preferably at about 600° C. When the carrier is silica, it isheated to at least 200° C., preferably about 200° C. to about 850° C.,and most preferably at about 600° C. The carrier material must have atleast some active hydroxyl (OH) groups on its surface to produce thecatalyst composition of this invention.

In the most preferred embodiment, the carrier is silica which, prior tothe use thereof in the first catalyst synthesis step, has beendehydrated by fluidizing it with nitrogen and heating at about 600° C.for about 4-16 hours to achieve a surface hydroxyl group concentrationof about 0.7 millimoles per gram (mmol/g). The silica of the mostpreferred embodiment is a high surface area, amorphous silica (surfacearea=300 m²/g; pore volume of about 1.65 cm³/g), and it is a materialmarketed under the tradenames of Davison 952 or Davison 955 by theDavison Chemical Division of W. R. Grace and Company. The silica is inthe form of spherical particles, which are obtained by a spray-dryingprocess. As procured, these silicas are not calcined and thus must bedehydrated as indicated above.

The catalyst synthesis is undertaken under inert conditions in theabsence of water and of oxygen. First, the carrier material is slurriedin a non-polar solvent. Suitable non-polar solvents are alkanes, such asisopentane, isohexane, hexane, n-heptane, octane, nonane, and decane,although a variety of other materials including cycloalkanes, such ascyclohexane, aromatics, such as benzene, toluene and ethylbenzene, mayalso be employed. The most preferred non-polar solvent is isopentane.

Prior to use, the non-polar solvent should be purified, such as bypercolation through silica gel and/or molecular sieves, to remove tracesof water, oxygen, polar compounds, and other materials capable ofadversely affecting catalyst activity. The slurry of the carriermaterial is prepared by introducing the carrier into the solvent,preferably while stirring, and heating the mixture to a temperature notexceeding 90° C., preferably to 40-60° C. The temperature of the slurryis critical with respect to the activity of the non-metallocenetransition metal which is subsequently added: if the temperature of thisslurry exceeds 90° C., it will result in deactivation of the transitionmetal component added subsequently. Accordingly, all catalyst precursorsynthesis steps are conducted below 90° C.

The slurry is contacted with at least one organomagnesium compound,while the heating is continued as indicated.

The organomagnesium compound has the empirical formula

R_(m)MgR′_(n)

where R and R′ are the same or different C₂-C₁₂ alkyl groups, preferablyC₄-C₁₀ alkyl groups, more preferably C₄-C₈ alkyl groups, and mostpreferably both R and R′ are mostly butyl groups, and m and n are each0, 1 or 2, providing that m+n is equal to the valence of Mg.

In the most preferred embodiment of the synthesis of this catalyst it isimportant to add only such an amount of the organomagnesium compoundthat will be deposited—physically or chemically—onto the support sinceany excess of the organomagnesium compound in the solution may reactwith other synthesis chemicals and precipitate outside of the support.The carrier drying temperature affects the number of sites on thecarrier available for the organomagnesium compound—the higher the dryingtemperature the lower the number of sites. Thus, the exact molar ratioof the organomagnesium compound to the hydroxyl groups will vary andmust be determined on a case-by-case basis to assure that only so muchof the organomagnesium compound is added to the solution as will bedeposited onto the support without leaving any excess of theorganomagnesium compound in the solution. Thus, the molar ratios givenbelow are intended only as an approximate guideline and the exact amountof the organomagnesium compound in this embodiment must be controlled bythe functional limitation discussed above, i.e., it must not be greaterthan that which can be deposited onto the support. If greater than thatamount is added to the solvent, the excess may react with thenon-metallocene transition metal compound, thereby forming a precipitateoutside of the support which is detrimental in the synthesis of ourcatalyst and must be avoided. The amount of the organomagnesium compoundwhich is not greater than that deposited onto the support can bedetermined in any conventional manner, e.g., by adding theorganomagnesium compound to the slurry of the carrier in the solvent,while stirring the slurry, until the organomagnesium compound isdetected in the solvent.

For example, for the silica carrier heated at about 600° C., the amountof the organomagnesium compound added to the slurry is such that themolar ratio of Mg to the hydroxyl groups (OH) on the solid carrier isabout 0.5:1 to about 4:1, preferably about 0.8:1 to about 3:1, morepreferably about 0.9:1 to about 2:1 and most preferably about 1:1. Theorganomagnesium compound dissolves in the non-polar solvent to form asolution from which the organomagnesium compound is deposited onto thecarrier.

It is also possible to add such an amount of the organomagnesiumcompound which is in excess of that which will be deposited onto thesupport, and then remove, e.g., by filtration and washing, any excess ofthe organomagnesium compound. However, this alternative is lessdesirable than the most preferred embodiment described above.

The organomagnesium-treated support is contacted with an organic alcohol(ROH) which is capable of displacing alkyl groups on the magnesium atom.The amount of the alcohol is effective to provide a ROH:Mg molar ratioof 0.5 to 2.0, preferably 0.8 to 1.5 and most preferably 0.90 to 1.0.

Contact of the silica-supported magnesium compound with the alcohol isalso undertaken in the slurry, at a temperature ranging from 25° C. to80° C., preferably 40° C. to 70° C.

The alkyl group in the alcohol can contain from 1 to 12 carbon atoms,preferably from 2 to 8; in the embodiments below, it is an alkyl groupcontaining 2 to 4 carbon atoms, particularly 4 carbon atoms (butylgroup). The inclusion of the alcohol addition step in the catalystsynthesis of the invention produces a catalyst which, relative to theabsence of this step, is much more active and requires a much lowerconcentration of the non-metallocene transition metal (e.g. titanium).

Also, the inclusion of the alcohol addition step in the catalystsynthesis provides a HMW polymer component with a relatively narrow MWDrelative to the HMW polymer component produced with a catalyst preparedwithout the alcohol addition step. A HMW polymer component with arelatively narrow MWD is required in a resin with a bimodal MWD in orderto produce a resin with good bubble stability in the film-formingprocess.

After the addition of the alcohol to the slurry is completed, the slurryis contacted with the first transition metal source, a non-metallocenetransition metal compound. Again, the slurry temperature must bemaintained at about 25 to about 70° C., preferably to about 40 to about60° C. Suitable non-metallocene transition metal compounds used hereinare compounds of metals of Groups 4A, and 5A, of the Periodic Chart ofthe Elements, as published by Chemical and Engineering News, 63(5), 27,1985, providing that such compounds are soluble in non-polar solvents.Non-limiting examples of such compounds are titanium and vanadiumhalides, e.g., titanium tetrachloride, vanadium tetrachloride, vanadiumoxytrichloride, or titanium and vanadium alkoxides, wherein the alkoxidemoiety has a branched or unbranched alkyl radical of 1 to about 20carbon atoms, preferably 1 to about 6 carbon atoms. The preferredtransition metal compounds are titanium compounds, preferablytetravalent titanium compounds. The most preferred titanium compound istitanium tetrachloride. The amount of the titanium or vanadium componentranges from a molar ratio with respect to Mg of 0.3 to 1.5, preferablyfrom 0.50 to 0.80.

Mixtures of non-metallocene transition metal compounds may also be usedand generally no restrictions are imposed on the transition metalcompounds which may be included. Any transition metal compound that maybe used alone may also be used in conjunction with other transitionmetal compounds.

After the addition of the non-metallocene transition metal compound iscomplete, the precursor remains in the slurry. It is treated with threeadditional ingredients, a trialkylaluminum compound AlR₃, a metallocenecomplex, and methylalumoxame (MAO).

The metallocene complex is added after or concurrently with thetrialkylaluminum compound. The introduction of the trialkylaluminumcompound is a critical component in this synthesis as it improves theproductivity of the bimetallic catalyst.

Preferably, the alkylaluminum compound is a trialkylaluminum compound inwhich the alkyl groups contain 1 to 10 carbon atoms, e.g. methyl, ethyl,propyl, i-propyl, butyl, isobutyl, pentyl, isopentyl, hexyl, isohexyl,heptyl, isoheptyl, octyl, or isooctyl. Most preferably, this componentis trimethylaluminum. The molar ratio of the trialkyaluminum compound totransition metal compound provided by the metallocene compound, canrange from 0.50 to 50, preferably from 1.0 to 20, and most preferablyfrom 2.0 to 15. The amount of the trialkylaluminum compound used incombination with the metallocene transition metal source is sufficientto increase the productivity of the catalysts.

The metallocene compound has the formula Cp_(x)MA_(y)B_(z) in which Cpis an unsubstituted or substituted cyclopentadienyl group, M iszirconium or hafnium atom and A and B belong to the group including ahalogen atom, hydrogen atom or an alkyl group. In the above formula ofthe metallocene compound, the preferred transition metal atom M iszirconium. In the above formula of the metallocene compound, the Cpgroup is an unsubstituted, a mono- or a polysubstituted cyclopentadienylgroup: and x is at least 1 and preferably is 2. The substituents on thecyclopentadienyl group can be preferably straight-chain C₁-C₆ alkylgroups. The cyclopentadienyl group can be also a part of a bicyclic or atricyclic moiety such as indenyl, tetrahydroindenyl, fluorenyl or apartially hydrogenated fluorenyl group, as well as a part of asubstituted bicyclic or tricyclic moiety. In the case when x in theabove formula of the metallocene compound is equal to 2, thecyclopentadienyl groups can be also bridged by polymethylene ordialkylsilane groups, such as —CH₂—, —CH₂—CH₂—, —CR′R″— and—CR′R″—CR′R″— where R′ and R″ are short alkyl groups or hydrogen atoms,—Si(CH₃)₂—, —Si(CH₃)₂—CH₂—CH₂—Si(CH₃)₂— and similar bridge groups. Ifthe A and B substituents in the above formula of the metallocenecompound are halogen atoms, they belong to the group of fluorine,chlorine, bromine or iodine; and y+z is 3 or less, provided that x+y+zequals the valence of M. If the substituents A and B in the aboveformula of the metallocene compound are alkyl groups, they arepreferably straight-chain or branched C₁-C₈ alkyl groups, such asmethyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, n-pentyl, n-hexylor n-octyl.

Suitable metallocene compounds include bis(cyclopentadienyl)metaldihalides, bis(cyclopentadienyl)metal hydridohalides,bis(cyclopentadienyl)metal monoalkyl monohalides,bis(cyclopentadienyl)metal dialkyls and bis(indenyl)metal dihalideswherein the metal is zirconium or hafnium atom, halide groups arepreferably chlorine and the alkyl groups are C₁-C₆ alkyls. Illustrative,but non-limiting examples of metallocenes includebis(cyclopentadienyl)zirconium dichloride, bis(cyclopentadienyl)hafniumdichloride, bis(cyclopentadienyl)zirconium dimethyl,bis(cyclopentadienyl)hafnium dimethyl, bis(cyclopentadienyl)zirconiumhydridochloride, bis(cyclopentadienyl)hafnium hydridochloride,bis(n-butylcyclopentadienyl) zirconium dichloride,bis(n-butylcyclopentadienyl) hafnium dichloride,bis(n-butylcyclopentadienyl) zirconium dimethyl,bis(n-butylcyclopentadienyl) hafnium dimethyl,bis(n-butylcyclopentadienyl) zirconium hydridochloride,bis(n-butylcyclopentadienyl) hafnium hydridochloride,bis(pentamethylcyclopentadienyl)zirconium dichloride,bis(pentamethylcyclopentadienyl)hafnium dichloride,cyclopentadienyl-zirconium trichloride, bis(indenyl)zirconiumdichloride, bis(4,5,6,7-tetrahydro-1-indenyl)zirconium dichloride, andethylene-[bis(4,5,6,7-tetrahydro-1-indenyl)] zirconium dichloride. Thebimetallic catalyst precursors of the invention may be prepared using aZr component prepared by pre-mixing the zirconium complex, e.g.,(n-BuCp)₂ZrCl₂ with TMA. Some metallocene complexes, although scarcelysoluble in paraffinic hydrocarbons, can be readily dissolved in them inthe presence of a trialkylaluminum compound.

MAO is also introduced into the slurry of the carrier. Preferably, it isadded either concurrently with the metallocene complex or after themetallocene addition. If MAO is introduced with the metallocene complex,then the trialkylaluminum compound, e.g. trimethylaluminum, should bepreviously introduced into the slurry, If the alumoxane is introducedinto the slurry after the metallocene complex, then the metallocenecomplex should be treated with the trialkylaluminum compound, e.g.trimethylaluminum, prior to the addition of MAO. In this embodiment, theamount of Al, provided by MAO, is sufficient to provide an[Al]:[transition metal] provided by the metallocene molar ratio rangingfrom 50 to 500, preferably 75 to 300.

Finally, the solvent is removed from the impregnated catalyst precusorby heating and/or under a positive pressure induced by an inert gas,such as nitrogen, at 40-50° C. The conditions in this step are closelycontrolled to reduce or eliminate agglomeration of impregnated catalystparticles and/or crosslinking of the alumoxane. Although solvent can beremoved by evaporation at relatively higher temperatures than thatdefined by the range above 40° C. and below about 50° C., very shortheating times schedules must be employed.

The molar ratio of alumoxane provided by aluminum, expressed as Al, tometallocene metal expressed as M (e.g. Zr), ranges from 50 to 500,preferably 75 to 300, and most preferably 100 to 200. In a preferredembodiment, the alumoxane and the metallocene compound are mixed at atemperature of about 20 to 80° C., for 0.1 to 6.0 hours prior to use.The solvent for the metallocene and alumoxane mixture can be aromatichydrocarbons, halogenated aromatic hydrocarbons, ethers, cyclic ethersor esters, preferably it is toluene.

In the most preferred embodiment, the metallocene component is mixedwith a trialkylaluminum compound such as TMA in a paraffinic hydrocarboncontaining 5 to 12 carbon atoms, preferably isopentane, isohexane,hexane and heptane, in the absence of MAO. This mixture is then added tothe titanium catalyst component. The MAO is added as a toluene solutionas the final step in the catalyst preparation. The catalyst precursorformed from the organomagnesium compound, the non-metallocene transitionmetal compound and the activated metallocene complex, must be activatedwith a cocatalyst, which is an alkylaluminum compound free of water andan alumoxane. The cocatalyst is preferably a trialkylaluminum compound,preferably it is TMA. The amount of TMA is sufficient to give an Al:Timolar ratio of about 10:1 to about 1000:1, preferably about 15:1 toabout 300:1, and most preferably about 20:1 to about 100:1.

The catalyst precursor of this invention is in particulate form; it canbe fed to the fluidized bed reactor for gas phase polymerizations andcopolymerizations of ethylene in the absence of additional alumoxane fedas a separate component to the fluidized-bed reactor.

EXAMPLES

Catalyst Precursor Preparation

Example 1

Into a Schlenk flask were added Davison-grade 955 silica (2.00 g), whichwas previously calcined at 600° C. for 4 h, and heptane (60 ml). Theflask was placed into an oil bath kept at 55° C. Dibutylmagnesium (1.44mmol) was added to the stirred silica slurry at 55° C. and stirring wascontinued for 1 h. 1-Butanol (1.368 mmol; butanol/Mg molar ratio of0.95) was added at 55° C. and the mixture was stirred for another 1 h.Then TiCl₄ (0.864 mmol) was added at 55° C. to the reaction medium andstirring was continued for 1 h. The flask was removed from the oil bathand allowed to cool to ambient temperature. Then a heptane solution (1.8ml) containing TMA (2.38 mmol) and (n-BuCp)₂ZrCl₂ (0.1904 mmol, 0.077 g)was added to the mixture. After stirring for 1 h, MAO (19.04 mmol Al) intoluene solution was added to the mixture and stirring was continued for0.6 h. Then the flask was placed into an oil bath at 55° C. and thesolvent mixture was removed under a nitrogen purge to give afree-flowing brown powder.

Example 2

The catalyst precursor was prepared as in Example 1 up to and includingthe TiCl₄ step. After removing the flask from the oil bath and allowingit to cool to ambient temperature, a toluene solution (4.4 ml)containing MAO (19.04 mmol Al) and (n-BuCp)₂ZrCl₂ (0.1904 mmol, 0.077 g)was added to the mixture. After stirring for 1 h, the flask was placedinto an oil bath (50° C.) and the solvents were removed under a nitrogenpurge to give a free-flowing brown powder.

Example 3

The catalyst precursor was prepared as in Example 1 up to and includingthe TiCl₄ step. After removing the flask from the oil bath and allowingit to cool to ambient temperature, TMA (2.38 mmol) was added to themixture. After stirring for 1 h, a toluene solution (4.4 ml) containingMAO (19.04 mmol Al) and (n-BuCp)₂ZrCl₂ (0.1904 mmol, 0.077 g) was addedto the mixture. After stirring for 1 h, the flask was placed into an oilbath (50° C.) and the solvents were removed under a nitrogen purge togive a free-flowing brown powder.

Example 3A

Into a Schlenk flask were added Davison-grade 955 silica (2.50 g), whichwas previously calcined at 600° C. for 4 h, and heptane (90 ml). Theflask was placed into an oil bath kept at 50° C. Dibutylmagnesium (1.80mmol) was added to the stirred silica slurry at 49° C. and stirring wascontinued for about 1 h. 1-Butanol (2.16 mmol; butanol/Mg molar ratio of1.2) was added at 49° C. and the mixture was stirred for 1 h. Then TiCl₄(1.08 mmol) was added at 49° C. to the reaction medium and stirring wascontinued for 1 h. The flask was removed from the oil bath and allowedto cool to room temperature. Then a heptane solution of TMA (4.30 mmol)was added to the flask and stirring was continued for 1 h. Finally, atoluene solution of MAO (20.30 mmol Al) containing (n-BuCp)₂ZrCl₂ (0.203mmol) was added to the slurry. Then all solvents were removed with astream of nitrogen to produce a free-flowing powder.

Example 4

The catalyst precursor was prepared as in Example 1 up to and includingthe TiCl₄ step. After removing the flask from the oil bath and allowingit to cool to ambient temperature, MAO in toluene solution (19.04 mmolAl) was added to the mixture.

After stirring for 1 h, a heptane solution (1.8 ml) containing TMA (2.38mmol) and (n-BuCp)₂ZrCl₂ (0.1904 mmol, 0.077 g) was added to the mixtureat ambient temperature. Then the flask was placed into an oil bath (55°C.); and the solvents were removed under a nitrogen purge to give afree-flowing brown powder.

Example 5

The catalyst precursor was prepared as in Example 1 excepttriethylaluminum (TEAL, 2.38 mmol) was used in place of TMA.

The preparative scheme for Examples 1-5 are illustrated below.

Example 1

Example 2

Example 3 and 3A

Example 4

Example 5

Some embodiments of the present invention involve the use of metallocenecomplex solutions in paraffinic hydrocarbons (Examples 1, 4, and 5). Allmetallocene complexes are practically insoluble in such liquids bythemselves but some of them become soluble when contacted withtrialkylaluminum compounds.

Example 6

0.1904 mmol (0.077 g) of (n-BuCp)₂ZrCl₂ was added to a 10-ml serumbottle, flushed with nitrogen followed by addition of 1.8 ml of TMAsolution in heptane (2.38 mmol). The metallocene complex quicklydissolved to form a yellow solution.

Example 7

0.230 mmol (0.0933 g) of (n-BuCp)₂ZrCl₂ was added to an NMR tube,flushed with nirtogen followed by addition of 2 ml of n-heptane. Themetallocene complex did not dissolve. Then, 2.3 ml of TMA solution inheptane (1.70 mmol) was added to the tube. The metallocene complexquickly dissolved. The ¹³C NMR spectrum of the solution was recorded andcompared to the spectrum of the pure (n-BuCp)₂ZrCl₂ complex (solution indeuterated chloroform). Whereas the spectrum of pure (n-BuCp)₂ZrCl₂contains only three signals in the Cp carbon atom range, at −135.2,−116.8 and −112.4 ppm, the spectrum of the contact product from(n-BuCp)₂ZrCl₂ and TMA contains eight signals at −135.5, −131.7, −117.0,−114.8, −112.5, −112.0, −110.6 and −108.8 ppm. This difference provesthat the (n-BuCp)₂ZrCl₂-TMA contact product is a unique entity.

Example 8

Dissolution of (n-BuCp)₂ZrCl₂ in heptane was carried out as in Example 6except that 2.38 mmol of TEAL was used in place of TMA. The metallocenecomplex rapidly dissolved to form a yellow solution.

Example 9

0.272 mmol (0.1097 g) of (n-BuCp)₂ZrCl₂ was added to an NMR tube,flushed with nitrogen followed by addition of 2 ml of n-heptane. Themetallocene complex did not dissolve. Then, 2.0 ml of TEAL solution inheptane (3.06 mmol) was added to the tube. The metallocene complexquickly dissolved. The ¹³C NMR spectrum of the solution was recorded andcompared to the spectrum of pure (n-BuCp)₂ZrCl₂. The spectrum of thecontact product from (n-BuCp)₂ZrCl₂ and TEAL contains fifteen signals inthe Cp carbon atom area encompassing the −126.2 -—104.4 ppm range. Thisdifference with the spectrum of pure (n-BuCp)₂ZrCl₂ (see Example 7)proves that the (n-BuCp)₂ZrCl₂-TEAL contact product is a unique entity.

Example 10

An attempt of dissolution of Cp₂ZrCl₂ in heptane was carried out as inExample 6. 0.1904 mmol (0.056) of Cp₂ZrCl₂ was used instead of(n-BuCp)₂ZrCl₂. In this case, however, the metallocene complex remainedinsoluble, hence, a catalyst preparation technique similar to that ofExamples 1, 4 and 5 cannot be applied with this complex.

Slurry Polymerization Reactions

Ethylene/1-hexene copolymers were prepared with the bimetallic catalystprecursors and the cocatalyst TMA. An example is given below.

A 1.6 liter stainless-steel autoclave equipped with a magnet-driveimpeller stirrer was filled with heptane (750 ml) and 1-hexene (30 ml)under a slow nitrogen purge at 50° C. and then 2.0 mmol of TMA wasadded. The reactor vent was closed, the stirring was increased to 1000rpm, and the temperature was increased to 95° C. The internal pressurewas raised 6.0 psi with hydrogen and then ethylene was introduced tomaintain the total pressure at 204 psig. After that, the temperature wasdecreased to 85° C., 37.6 mg of the catalyst precursor of Example 1 wasintroduced into the reactor with ethylene over-pressure, and thetemperature was increased and held at 95° C. The polymerization reactionwas carried out for 1 h and then the ethylene supply was stopped. Thereactor was cooled to ambient temperature and the polyethylene wascollected.

The slurry polymerization results for these catalysts are given below.

Productivity Flow Index Catalyst Precursor g/g-h (I₂₁) MFR Example 13310 19.4 139 Example 2 2170 29.7 138 Example 3 3080 18.4 142 Example 3A3300 2.0 54 Example 4 1670 9.2 82 Example 5 1820 3.4 57

All the catalyst systems produce resins with bimodal MWDs. Relativecontributions of the components can be judged by the flow index of theresin: the higher the flow index, the higher the contribution of the Zrcomponent. The efficiency of the Zr component is much higher for thecatalyst systems of Examples 1-3, as evident from their higher resinflow indexes. Adding TMA prior to the addition of MAO in the catalystprecursor preparation resulted in the most active catalysts (Examples1,3). In contrast, adding MAO before TMA addition in the catalystprecursor preparation (Example 4) had a deleterious effect on thecatalyst productivity. The catalyst precursors of Examples 1 and 4 areunique in that the (n-BuCp)₂ZrCl₂ complex is reacted with TMA and notpre-mixed with MAO. Using TEAL (Example 5) in place of TMA in thecatalyst precursor preparation produced a catalyst system with low Zrefficiency as manifested by a low resin flow index.

Thus it is apparent that there has been provided, in accordance with theinvention, a synthesis, that fully satisfies the objects, aims, andadvantages set forth above. While the invention has been described inconjunction with specific embodiments thereof, it is evident that manyalternatives, modifications, and variations will be apparent to thoseskilled in the art in light of the foregoing description. Accordingly,it is intended to embrace all such alternatives, modifications, andvariations as fall within the spirit and broad scope of the appendedclaims.

What is claimed is:
 1. A contact product comprising a metallocenecomplex and a trialkylaluminum compound, wherein said metallocenecomplex contains one or two substituted cyclopentadienyl groups and atransition metal selected from the group consisting of titanium,zirconium and hafnium; wherein said trialkylaluminum compound containslinear or branched alkyl groups from C₁ to C₈; and wherein said contactproduct is soluble in paraffinic hydrocarbon solvents.
 2. The contactproduct of claim 1, wherein said metallocene complex isbis(n-butylcyclopentadienyl) zirconium dichloride.
 3. The contactproduct of claim 1, wherein said trialkylaluminum compound istrimethylaluminum.